Push-pull sound reproducing method and system



p 1945- A. BADMAIEFF 2,385,324

' PUSH-PULL SOUND REPRODUCING METHOD AND SYSTEM Filed Sept. 10, 1943 1449 15 BADMA/EFE; INVENTOR ATTORNEY.

Patented Sept. 25, 1945 PUSH-PULL SOUND REPRODUOIN G METHOD AND SYSTEM Alexis Badmaiefl', Indianapolis, Ind., assignor to Radio Corporation of America, a corporation of Delaware Application September 10, 1943, Serial No. 501,778

9 Claims. ((ll. 179-1003) This invention relates to sound reproducing systems and particularly to the reproduction of sound from push-pull photographic sound records wherein the light beam is projected to a divided photoelectric cell or two separate photoeilelctric cells connected in a push-pull relations p.

It is well-known in the production of photographic sound records to accompany motion pictures, that there are several types of records which may be made depending upon the type of light beam modulating system employed. For instance, a single'unilateral type of record is disclosed in McDowell Patent No. 1,855,197 of. April 26, 1932, while a bilateral type of record is shown in Fig. 3 of Patent No. 2,224,914 of December 17, 1940. The combination type of variable areavariable density bilateral record is shown in Fig. 2 of Patent No. 2,268,438 of December 30, 1941,

and push-pull types of records either Class A,

Class B, or Class A--B, are shown in Patent No. 2,217,154 of October 8, 1940, and 'Patent No. 2,311,159 of February 16, 1943. The first type of records require only a single photoelectric cell for their reproduction, while the push-pull types of records require either a divided cell or two separate cells connected in a push-pull circuit, the light beams through the two longitudinal components being separated by prisms and lenses. A system of this latter type, in which different colors are used to aid in separating the light passing through each longitudinal half of a pushpull sound record, is disclosed and claimed in Patent No. 2,292,062 of August 4, 1942.

The present invention is directed to a system for reproducing push-pull sound tracks wherein each portion of the total light beam or the particular beam passing through one longitudinal half of the sound record is, before impression on the record, characterized difierently from the other portion or beam passing through the other half of the record. The individual beams are characterized by polarizing each beam 90 degrees from the other, after which each respective cell is screened by a second light polarizing element of similar character and polarizing properties to prevent interference of the light beams on the cells. Since the screening element of each cell prevents the other beam from reaching that cell,

the light beams are separated without the use of lenses and prisms for this purpose.

The principal object of the invention, there fore, is to improve the reproduction of push-pull sound records.

Another object of the invention isto improve the separation and individualizing of light beams passing through each portion of a sound record.

A further object of the invention is to provide an improved method of facilitating the impression upon a photoelectric cell of the light passing through a portion of a sound record.

A further object of the invention is to provide improved means of individualizing light beams passing through portions of a push-pull sound record for impression on respective photoelectric cells.

Although the novel features which are believed to be characteristic of this invention will be pointed out with particularity in the appended claims, the mannerof its organization and the mode of its operation will be better understood by referring to the following description read in conjunction with the accompanying drawing, forming a part hereof, in which:

Fig. 1 is a diagrammatic view of theoptical portion of a sound reproducing system embodying the invention, and,

Fig. 2 is a detailed view showing the light beams as impressed upon the sound record.

Referring now to the drawing, a standard film 5 is shown with its picture area 6 and sound track portion 1 having a sound record thereon which may be any one of the above-mentioned pushpull types. A light source is shown at lo, a collecting lens at H, and a projecting lens at l2, while a pair of push-pull cells l5 and I6 are shown connected in a standard push-pull circuit having a polarizing source l1 and a transformer l8. The elements just described are the stand--v ard elements required in the usual push-pull reproducing system except for the necessary light dividing prisms.

Referring now to the remaining elements of Fig. 1, a mask 20 is shown with a standard slit 2| therein, but over which" is positioned Polaroid sheets 23 and 24, sheet 24 being positioned so that its axis of polarization is degrees from that of "Polaroid sheet 23. 24, and particularly the Junction line between the sheets, should be positioned as close as possible to the slit 2|, the junction line being at the center of the slit. The light passing through the slit 2|, therefore, will be formed into two beams polarized 90 degrees apart and at 45 degrees to the slit and focused by lens l2 on the film sound track, as shown in Fig. 2. These beams are varied in area'by the sound track modulations in the respective longitudinal portions of the record. Although one particular means of polarizing the beams is shown, it is to The sheets 23 and r be. understood that any other suitable polarizing elements, such Nicol and Foucault prisms and tourmaline crystals, may be employed. Furthermore, push-pull records of the variable density type may also be reproduced.

The emerging light beams from the record are impressed upon a second pair of Polaroid" sheets 28 and 21, which coverphotoelectric cells I and I6, respectively. By this arrangement, light from only one-half of the record 'I is impressed on one photoelectric cell and light from only the other half of the record will be impressed on the other cell. This separating isproduced because the light polarized by sheet 23 will only pass through sheet 26 to cell I5, and not through sheet 271 to cell It due to the 90 degree discrepancy in the polarization of sheets 23 and 21. Likewise the light through polariz ing sheet 24 will only pass through sheet 21 and not through sheet 26. Thus, no separating lenses or prisms are required to obtain the impression oi the proper beam on the proper cell.

I claim a my invention:

1. In a sound reproducing system, a sound record having two longitudinal components, a source of light for impression on said sound record, means for forming said light into a plurality .of difierently characterized beams before impression on said sound record, a photoelectric cell upon which each of said beams is to be impressed, and means positioned in said light beam after passage through each side of said record for preventing any portion of any one of said beams from being impressed on the same cell.

2..A sound reproducing system in accordance with claim 1 in which said characterizing means light to each specific photoelectric cell after passage through said record.

5. A sound reproducing system in accordance with claim 4 in which said characterized means constitutes a pair of "Polaroid elements for Dolarizing said components 90 degrees apart.

6. A sound reproducing system for reproducing a record having a pair of longitudinal components, a light source, means for forming a pair of light beams from said source, said means polarizing one ofsaid beams at 90 degrees from the polarization of the other of said beams, means for projecting one of said beams on one of said longitudinal components and the other of said beams on the other of said components, a pair of photoelectric cells, one cell being adapted to receive th light of. one or said beams after modulaticn by one of said record components, and

the other cell being adapted to receive the light of the other of said beams after modulation by venting either cell from receiving light of both 3. A sound reproducing system in accordance ponent record comprising a source of light, a

plurality of photoelectric cells, and means for passing a light beam through each component of said record for impression on an individual photoelectric cell, said means including means of said beams.

l. A sound reproducing system in accordance with claim 6 in which said last mentioned means includes a polarization element for each beam to obstruct passage of light of, said other beam.

8. The method of separating a pair of light beams for individually and separately scanning a pair of longitudinal record components and individually and separately detecting each of said components by a respective number of photoelectric cells comprising polarizing each of said light beams degrees apart, projecting each of said diflerently polarized beams to a respective film record component, and similarly polarizing each of said beamsiafter passage through said respectiv fllm record component and before impression on said respective cells.

9. The method in accordance with claim 8 in which eachof said polarized beams is focused on its respective film record component and is modulated thereby, each of said modulated beams being given the same polarization before the detection thereof.

' ALEmS BADMAIEFF. 

